Benefits from a multi-receiver architecture for GNSS precise positioning

Precise positioning with a stand-alone GPS receiver or using differential corrections is known to be strongly degraded in an urban or sub-urban environment due to frequent signal masking, strong multipath effect, frequent cycle slips on carrier phase, etc. The objective of this Ph.D. thesis is to explore the possibility of achieving precise positioning with a low-cost architecture using multiple installed low-cost single-frequency receivers with known geometry whose one of them is RTK positioned w.r.t an external reference receiver. This setup is thought to enable vehicle attitude determination and RTK performance amelioration. In this thesis, we firstly proposed a method that includes an array of receivers with known geometry to enhance the performance of the RTK in different environments. Taking advantage of the attitude information and the known geometry of the installed array of receivers, the improvement of some internal steps of RTK w.r.t an external reference receiver can be achieved. The navigation module to be implemented in this work is an Extended Kalman Filter (EKF). The performance of a proposed two-receiver navigation architecture is then studied to quantify the improvements brought by the measurement redundancy. This concept is firstly tested on a simulator in order to validate the proposed algorithm and to give a reference result of our multi-receiver system’s performance. The pseudorange measurements and carrier phase measurements mathematical models are implemented in a realistic simulator. Different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array, the satellite constellation geometry, and the amplitude of the noise measurement, in order to determine the influence of the use of an array of receivers. The simulation results show that our multi-receiver RTK system w.r.t an external reference receiver is more robust to noise and degraded satellite geometry, in terms of ambiguity fixing rate, and gets a better position accuracy under the same conditions when compared with the single receiver system. Additionally, our method achieves a relatively accurate estimation of the attitude of the vehicle which provides additional information beyond the positioning. In order to optimize our processing, the correlation of the measurement errors affecting observations taken by our array of receivers has been determined. Then, the performance of our real-time single frequency cycle-slip detection and repair algorithm has been assessed. These two investigations yielded important information so as to tune our Kalman Filter. The results obtained from the simulation made us eager to use actual data to verify and improve our multi-receiver RTK and attitude system. Tests based on real data collected around Toulouse, France, are used to test the performance of the whole methodology, where different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array as well as the environmental conditions (open sky, suburban, and constrained urban environments). The thesis also tried to take advantage of a dual GNSS constellation, GPS and Galileo, to further strengthen the position solution and the reliable use of carrier phase measurements. The results show that our multi-receiver RTK system is more robust to degraded GNSS environments. Our experiments correlate favorably with our previous simulation results and further support the idea of using an array of receivers with known geometry to improve the RTK performance

GNSS precise point positioning :the enhancement with GLONASS

PhD ThesisPrecise Point Positioning (PPP) provides GNSS navigation using a stand-alone receiver with no base station. As a technique PPP suffers from long convergence times and quality degradation during periods of poo satellite visibility or geometry. Many applications require reliable realtime centimetre level positioning with worldwide coverage, and a short initialisation time. To achieve these goals, this thesis considers the use of GLONASS in conjunction with GPS in kinematic PPP. This increases the number of satellites visible to the receiver, improving the geometry of the visible satellite constellation. To assess the impact of using GLONASS with PPP, it was necessary to build a real time mode PPP program. pppncl was constructed using a combination of Fortran and Python to be capable of processing GNSS observations with precise satellite ephemeris data in the standardised RINEX and SP3 formats respectively. pppncl was validated in GPS mode using both staticsites and kinematic datasets.In GPS only mode,one sigma accuracy of 6.4mm and 13mm in the horizontal and vertical respectively for 24h static positioning was seen. Kinematic horizontal and vertical accuracies of 21mm and 33mm were demonstrated. pppncl was extended to assess the impact of using GLONASS observations in addi- tion to GPS instatic and kinematic PPP. Using ESA and Veripos Apex G2 satel- lite orbit and clock products,the average time until 10cm 1D static accuracy was achieved, over arange of globally distributed sites, was seen to reduce by up to 47%. Kinematic positioning was tested for different modes of transport using real world datasets. GPS/GLONAS SPPP reduced the convergence time to decimetre accuracy by up to a factor of three. Positioning was seen to be more robust in comparison to GPS only PPP, primarily due to cycle slips not being present on both satellite systems on the occasions when they occurred,and the reduced impact of undetected outliersEngineering and Physical Sciences Research Council, Verip os/Subsea

센티미터 급 광역 보강항법 시스템의 반송파 위상 기반 보정정보 생성 알고리즘에 관한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부,2020. 2. 기창돈.Recently, the demand for high-precision navigation systems for centimeter-level service has been growing rapidly for various Global Navigation Satellite System (GNSS) applications. The network Real-Time Kinematic (RTK) is one of the candidate solution to provide high-accuracy position to user in real-time. However, the network RTK requires a lot of reference stations for nationwide service. Furthermore, it requires high-speed data-link for broadcasting their scalar-type corrections. This dissertation proposed a new concept of satellite augmentation system called Compact Wide-Area RTK, which provides centimeter-level positioning service on national or continental scales to overcoming the limitation of the legacy network RTK methods. Using the wide-area network of multiple reference stations whose distance is 200~1,000 km, the proposed system generates three types of carrier-phase-based corrections: satellite orbit corrections, satellite code/phase clock (CPC) corrections, tropospheric corrections. Through the strategy of separating the scalar-type corrections of network RTK into vector forms of each error component, it is enable to expand network RTK coverage to continental scale using a similar number of reference stations as legacy meter-level Satellite-Based Augmentation System (SBAS). Furthermore, it is possible to broadcast their corrections over a wide-area using geosynchronous (GEO) satellite with extremely low-speed datalink of 250 bps likewise of legacy SBAS. To sum up, the proposed system can improve position accuracy by centimeter-level while maintaining the hardware infrastructure of the meter-level legacy SBAS. This study mainly discussed on the overall system architecture and core algorithms for generating satellite CPC corrections and tropospheric corrections. This study proposed a new Three-Carrier Ambiguity Resolution (TCAR) algorithm using ionosphere-free combinations to correctly solve the integer ambiguity in wide-area without any ionospheric corrections. The satellite CPC corrections are calculated based on multiple stations for superior and robust performance under communication delay and outage. The proposed algorithm dramatically reduced the latency compensation errors and message amounts with compare to conventional RTK protocols. The tropospheric corrections of the compact wide-area RTK system are computed using GPS-estimated precise tropospheric delay and weather data based model together. The proposed algorithm adopts spherical harmonics function to significantly reduce the message amounts and required number of GPS reference stations than the network RTK and Precise Point Positioning-RTK (PPP-RTK), while accurately modeling the spatial characteristic of tropospheric delay with weather data together. In order to evaluate the user domain performance of the compact wide-area RTK system, this study conducted the feasibility test on mid-west and south USA using actual GPS measurements. As a result, the 95% horizontal position error is about 1.9 cm and the 95% vertical position error is 7.0 cm after the integer ambiguity is correctly fixed using GPS-only signals. The user ambiguity resolution takes about 2 minutes, and success-fix rate is about 100 % when stable tropospheric condition. In conclusion, the compact wide-area RTK system can provide centimeter-level positioning service to wide-area coverage with extremely low-speed data link via GEO satellite. We hope that this new system will consider as candidate solution for nationwide centimeter-level service such as satellite augmentation system of the Korea Positioning System (KPS).최근 자율주행자동차, 무인 드론 배송, 충돌 회피, 무인트랙터를 이용한 스마트 무인 경작 등 위성항법시스템(GNSS, Global Navigation Satellite System)을 사용하는 다양한 응용분야에서 수 cm 수준의 정밀 위치 정보에 대한 요구가 급격히 증가하고 있다. 본 학위논문에서는 1 m 급의 정확하고 신뢰성 높은 위치 서비스를 제공하는 기존의 정지궤도위성 기반 광역 보강항법 시스템(SBAS, Satellite-Based Augmentation System)의 기준국 인프라를 유지하면서 항법 성능을 수 cm 수준으로 향상시키기 위해 반송파 위상 기반의 초정밀 보정정보 생성 알고리즘에 관한 연구를 수행하였다. 실시간 정밀 측위(RTK, Real-Time Kinematic)는 반송파 위상 측정치에 포함된 미지정수를 정확하게 결정하여 수 cm 수준의 정밀 항법 서비스를 가능하게 하는 대표적인 기법이다. 그 중에서도 약 50~70 km 간격으로 분포된 다수의 기준국 정보를 활용하는 Network RTK 기법은 동적 사용자의 빠르고 정확한 위치 결정이 가능한 인프라로서 주목받고 있다. 하지만 스칼라 형태로 구성된 Network RTK 보정정보는 각 기준국 별로 관측된 위성 수에 따라 생성이 되기 때문에 보정 데이터 량이 상당히 방대하다. 메시지 전송에 필요한 데이터 량이 많을수록 고속의 통신 환경을 필요로 하며, 메시지 시간 지연이나 통신 단절에 매우 취약한 문제를 가지고 있다. 또한 스칼라 형태의 보정정보는 사용자와 기준국 간의 거리가 멀어질수록 보정 오차가 크게 발생하기 때문에 대륙 혹은 나라 규모의 광역에서 서비스하기 위해서는 수십~수백 개 이상의 기준국 인프라 구축이 필수적이다. 예를 들어, SBAS가 한반도 지역 서비스를 위해 5~7개의 기준국이 필요한 반면 Network RTK는 90~100개의 기준국이 필요하다. 즉 Network RTK는 시스템 구축 및 유지 비용이 SBAS 대비 약 15배 정도 많이 들게 된다. 본 논문에서는 기존 Network RTK의 문제점을 해결하기 위한 방법으로 대륙 급 광범위한 영역에서 실시간으로 cm급 초정밀 위치결정 서비스 제공이 가능한 Compact Wide-Area RTK 라는 새로운 개념의 광역보강항법시스템 아키텍처를 제안하였다. Compact Wide-Area RTK는 약 200~1,000 km 간격으로 넓게 분포된 기준국 네트워크를 활용하여 반송파 위상 기반의 정밀한 위성 궤도 보정정보, 위성 Code/Phase 시계 보정정보, 대류층 보정정보를 생성하는 시스템이다. 기존 스칼라 형태의 Network RTK 보정정보 대신 오차 요소 별 벡터 형태의 정밀 보정정보를 생성함으로써 데이터 량을 획기적으로 절감하고 서비스 영역을 확장할 수 있다. 최종적으로 SBAS와 마찬가지로 250 bps의 저속 통신 링크를 가진 정지궤도위성을 통해 광역으로 보정정보 방송이 가능하다. 본 논문에서는 3가지 보정정보 중 위성 Code/Phase 시계 보정정보와 대류층 보정정보 생성을 위한 핵심 알고리즘에 대해 중점적으로 연구하였다. 반송파 위상 기반의 정밀 보정정보 생성을 위해서는 먼저 미지정수를 정확하게 결정해야 한다. 본 논문에서는 삼중 주파수 반송파 위상 측정치의 무-전리층 조합을 활용하여 전리층 보정정보 없이도 정확하게 미지정수 결정 가능한 새로운 방법을 제안하였다. 위성 Code/Phase 시계 보정정보는 통신 지연 및 고장 시 우수하고 강건한 성능을 위해 다중 기준국의 모든 측정치를 활용하여 추정된다. 이 때 각 기준국 별 서로 다른 미지정수 때문에 발생하는 문제는 앞서 정확하게 결정된 기준국 간 이중차분 된 미지정수를 활용하여 수준을 조정하는 과정을 통해 해결이 가능하다. 그 결과 생성된 위성 Code/Phase 보정정보 메시지의 크기, 변화율, 잡음 수준이 크게 개선되었고, 통신 지연 시 오차 보상 성능이 기존 RTK 프로토콜 보다 99% 향상 됨을 확인하였다. 대류층 보정정보는 적은 수의 기준국 만을 활용하여 정확하게 대류층을 모델링하기 위해 자동 기상관측시스템으로부터 수집한 기상 정보를 추가로 활용하여 생성된다. 본 논문에서는 GNSS 기준국 네트워크로부터 정밀하게 추정된 반송파 위상 기반 수직 대류층 지연과 기상정보 기반으로 모델링 된 수직 대류층 지연을 함께 활용할 수 있는 새로운 알고리즘을 제안하였다. 구면조화함수를 사용하여 Network RTK 및 PPP-RTK 보다 필요한 메시지 양과 기준국 수를 크게 감소시키면서도 RMS 2 cm 수준으로 정확한 보정정보 생성이 가능함을 확인하였다. 본 논문에서 제안한 Compact Wide-Area RTK 시스템의 항법 성능을 검증하기 위해 미국 동부 지역 6개 기준국의 실측 GPS 데이터를 활용하여 테스트를 수행하였다. 그 결과 제안한 시스템은 미지정수 결정 이후 사용자의 95% 수평 위치 오차 1.9 cm, 95% 수직 위치 오차 7.0 cm 로 위치를 정확하게 결정하였다. 사용자 미지정수 결정 성능은 대류층 안정 상태에서 약 2분 내로 100% 의 성공률을 가진다. 본 논문에서 제안한 시스템이 향후 한국형 위성항법 시스템(KPS, Korean Positioning System)의 전국 단위 센티미터 급 서비스를 위한 알고리즘으로 활용되기를 기대한다.CHAPTER 1. Introduction 1 1.1 Motivation and Purpose 1 1.2 Former Research 4 1.3 Outline of the Dissertation 7 1.4 Contributions 8 CHAPTER 2. Overview of GNSS Augmentation System 11 2.1 GNSS Measurements 11 2.2 GNSS Error Sources 14 2.2.1 Traditional GNSS Error Sources 14 2.2.2 Special GNSS Error Sources 21 2.2.3 Summary 28 2.3 GNSS Augmentation System 29 2.3.1 Satellite-Based Augmentation System (SBAS) 29 2.3.2 Real-Time Kinematic (RTK) 32 2.3.3 Precise Point Positioning (PPP) 36 2.3.4 Summary 40 CHAPTER 3. Compact Wide-Area RTK System Architecture 43 3.1 Compact Wide-Area RTK Architecture 43 3.1.1 WARTK Reference Station (WRS) 48 3.1.2 WARTK Processing Facility (WPF) 51 3.1.3 WARTK User 58 3.2 Ambiguity Resolution and Validation Algorithms of Compact Wide-Area RTK System 59 3.2.1 Basic Theory of Ambiguity Resolution and Validation 60 3.2.2 A New Ambiguity Resolution Algorithms for Multi-Frequency Signals 65 3.2.3 Extra-Wide-Lane (EWL) Ambiguity Resolution 69 3.2.4 Wide-Lane (WL) Ambiguity Resolution 71 3.2.5 Narrow-Lane (NL) Ambiguity Resolution 78 3.3 Compact Wide-Area RTK Corrections 83 3.3.1 Satellite Orbit Corrections 86 3.3.2 Satellite Code/Phase Clock (CPC) Corrections 88 3.3.3 Tropospheric Corrections 89 3.3.4 Message Design for GEO Broadcasting 90 CHAPTER 4. Code/Phase Clock (CPC) Correction Generation Algorithm 93 4.1 Former Research of RTK Correction Protocol 93 4.1.1 Observation Based RTK Data Protocol 93 4.1.2 Correction Based RTK Data Protocol 95 4.1.3 Compact RTK Protocol 96 4.2 Satellite CPC Correction Generation Algorithm 100 4.2.1 Temporal Decorrelation Error Reduced Methods 102 4.2.2 Ambiguity Level Adjustment 105 4.2.3 Receiver Clock Synchronization 107 4.2.4 Averaging Filter of Satellite CPC Correction 108 4.2.5 Ambiguity Re-Initialization and Message Generation 109 4.3 Correction Performance Analysis Results 111 4.3.1 Feasibility Test Environments 111 4.3.2 Comparison of RTK Correction Protocol 113 4.3.3 Latency Compensation Performance Analysis 116 4.3.4 Message Data Bandwidth Analysis 119 CHAPTER 5. Tropospheric Correction Generation Algorithm 123 5.1 Former Research of Tropospheric Correction 123 5.1.1 Tropospheric Corrections for SBAS 124 5.1.2 Tropospheric Corrections of Network RTK 126 5.1.3 Tropospheric Corrections of PPP-RTK 130 5.2 Tropospheric Correction Generation Algorithm 136 5.2.1 ZWD Estimation Using Carrier-Phase Observations 138 5.2.2 ZWD Measurements Using Weather Data 142 5.2.3 Correction Generation Using Spherical Harmonics 149 5.2.4 Correction Applying Method for User 157 5.3 Correction Performance Analysis Results 159 5.3.1 Feasibility Test Environments 159 5.3.2 Zenith Correction Domain Analysis 161 5.3.3 Message Data Bandwidth Analysis 168 CHAPTER 6. Compact Wide-Area RTK User Test Results 169 6.1 Compact Wide-Area RTK User Process 169 6.2 User Performance Test Results 173 6.2.1 Feasibility Test Environments 173 6.2.2 User Range Domain Analysis 176 6.2.3 User Ambiguity Domain Analysis 182 6.2.4 User Position Domain Analysis 184 CHAPTER 7. Conclusions 189 Bibliography 193 초 록 207Docto

Ps-LAMBDA: Ambiguity success rate evaluation software for interferometric applications

Integer ambiguity resolution is the process of estimating the unknown ambiguities of carrier-phase observables as integers. It applies to a wide range of interferometric applications of which Global Navigation Satellite System (GNSS) precise positioning is a prominent example. GNSS precise positioning can be accomplished anytime and anywhere on Earth, provided that the integer ambiguities of the very precise carrier-phase observables are successfully resolved. As wrongly resolved ambiguities may result in unacceptably large position errors, it is crucial that one is able to evaluate the probability of correct integer ambiguity estimation. This ambiguity success rate depends on the underlying mathematical model as well as on the integer estimation method used. In this contribution, we present the Matlab toolbox Ps-LAMBDA for the evaluation of the ambiguity success rates. It allows users to evaluate all available success rate bounds and approximations for different integer estimators. An assessment of the sharpness of the bounds and approximations is given as well. Furthermore, it is shown how the toolbox can be used to assess the integer ambiguity resolution performance for design and research purposes, so as to study for instance the impact of using different GNSS systems and/or different measurement scenarios

Trustworthy precise point positioning with global navigation satellite systems

With the modernization of the Global Navigation Satellite System (GNSS), GNSS precise point positioning (PPP) technology becomes popular benefiting from its wide coverage and high accuracy. However, PPP technology still has many challenges in terms of continuity, fast convergence, and integrity monitoring, and these unsolved issues result in limitations of engineering applications. In this thesis, a reliable PPP technology with GNSS is investigated. The main contributions of the thesis are as follows: (1) A new cycle slip repair method that uses multiple epochs of time-differencing and geometry-based observations are proposed which has a significant improvement in the success rate of cycle slip repairs compared to existing methods. The positioning results also reflect that this method can reduce position errors and improve the continuity of PPP technology. (2) A systematic comparison of current interpolation methods used for high-accuracy regional ionospheric corrections is presented. It is found that each method has essentially the same accuracy in a small regional network with only a few stations, while the Kriging interpolation method can significantly improve the accuracy when the size of the network increases. Besides, a new method for predicting the uncertainty after broadcasting by grid point is also proposed. It has been validated that it is significantly closer to reality than other existing methods. In addition, different ionospheric correction implementation methods at the user end are also compared. (3) A integrity monitoring scheme for use in PPP based on real-time kinematic (RTK) positioning networks (PPP-RTK) with regional atmospheric corrections has been developed, which is based on the impacts of faults on the estimators considering possible faults in undifferenced and uncombined measurements. (4) Procedures for integrity monitoring considering the risks caused by incorrect ambiguity fixing are investigated. Two different methods for considering the probability of wrong ambiguity fixing including categorizing it into unmonitored fault and categorizing it as an individual type of fault are proposed and analyzed. (5) An integrity monitoring (IM) scheme based on the single-epoch framework for PPP-RTK is also proposed in order to exclude the effects caused by using observations from multiple epochs. Different solutions and their related availability are evaluated based on the satellite geometry in the global area

A method for scintillation characterization using geodetic receivers operating at 1 Hz

Ionospheric scintillation produces strong disruptive effects on global navigation satellite system (GNSS) signals, ranging from degrading performances to rendering these signals useless for accurate navigation. The current paper presents a novel approach to detect scintillation on the GNSS signals based on its effect on the ionospheric-free combination of carrier phases, i.e. the standard combination of measurements used in precise point positioning (PPP). The method is implemented using actual data, thereby having both its feasibility and its usefulness assessed at the same time. The results identify the main effects of scintillation, which consist of an increased level of noise in the ionospheric-free combination of measurements and the introduction of cycle-slips into the signals. Also discussed is how mis-detected cycle-slips contaminate the rate of change of the total electron content index (ROTI) values, which is especially important for low-latitude receivers. By considering the effect of single jumps in the individual frequencies, the proposed method is able to isolate, over the combined signal, the frequency experiencing the cycle-slip. Moreover, because of the use of the ionospheric-free combination, the method captures the diffractive nature of the scintillation phenomena that, in the end, is the relevant effect on PPP. Finally, a new scintillation index is introduced that is associated with the degradation of the performance in navigation.Postprint (author's final draft

Robust GNSS Point Positioning in the Presence of Cycle Slips and Observation Gaps

Among the various factors limiting accurate positioning with a Global Navigation Satellite System (GNSS) is the inherent code error level on a code observation, cycle slip occurrence on a phase observation, inadequate accuracy in the broadcast ionospheric model for single-frequency receivers; and the occurrence of observation gaps, which are short duration satellite outages (temporal loss of an observed satellite). The existing Cycle Slip Detection and Correction (CSDC) techniques are usually multi-satellite based; quite computationally intensive; and are often marred by the inherent code errors from the included code observations. Also, existing code-carrier smoothing techniques employed to mitigate code errors are limited by cycle slip occurrences on phase observations. In this research, algorithms are proposed in order to facilitate simple, efficient and real-time cycle slip detection, determination and correction, on a standalone single- or dual-frequency receiver; to enable cycle-slip-resilient code errors mitigation; and to improve the broadcast ionospheric model for single-frequency receivers. The proposed single-satellite and phase-only-derived CSDC algorithms are based on adaptive time differencing of short time series phase observables. To further provide robustness to the impact of an observation gap occurrence for an observed satellite, post-gap ionospheric delay is predicted assuming a linearly varying ionospheric delay over a short interval, which consequently enables the dual-frequency post-gap cycle slip determination and code error mitigation. The proposed CSDC algorithms showed good performance, with or without simulated cycle slips on actual data obtained with static and kinematic GNSS receivers. Over different simulated cycle slip conditions, a minimum of 97.3% correct detection and 79.8% correctly fixed cycle slips were achieved with single-frequency data; while a minimum of 99.9% correct detection and 95.1% correctly fixed cycle slips were achieved with dual-frequency data. The point positioning results obtained with the proposed methods that integrates the new code error mitigation and cycle slip detection and correction algorithms, showed significant improvement over the conventional code-carrier smoothing technique (i.e. a standalone Hatch filter, without inclusion of any cycle slip fixing method). Under different simulated cycle slip scenarios, the new methods achieved 25-42% single-frequency positioning accuracy improvement over the standalone Hatch filter, and achieved 18-55% dual-frequency positioning accuracy improvement over the standalone Hatch filter

Carrier-phase based real-time static and kinematic precise point positioning Using GPS and GALILEO

Over the last few years, there has been a rising demand for sub-metre accuracy (and higher) for navigation and surveying using signals from Global Navigation Satellite Systems (GNSS). To meet this rising demand, many precise positioning techniques and algorithms using the carrier-phase observable have been developed. Currently, high accuracy Real-Time Kinematic (RTK) positioning is possible using relative or differential techniques which require one GNSS user receiver and at least one other as the reference (known) station within a certain distance from the user. Unlike these conventional differential positioning techniques, Precise Point Positioning (PPP) is based on processing carrier phase observations from only one GNSS receiver. This is more cost-effective as it removes the need for reference receivers and therefore, is not limited by baseline length. However, errors mitigated by ‘differencing’ in conventional methods must be modelled accurately and reliably for PPP. This thesis develops a PPP software platform in Matlab code and uses it to investigate the state-of-the-art PPP algorithms and develop enhancements. Specifically, it is well documented that conventional PPP algorithms suffer from long convergence periods ranging from thirty minutes (for static users) to hours (for dynamic users). Therefore, to achieve fast convergence, two approaches are developed in this thesis. Firstly, a combination of the state-of-the-art GNSS error models and new algorithms for measurement weighting, management of receiver clock jumps and assignment of a dynamic covariance factor, are exploited. Secondly, based on the results of the analysis of the quantitative relationships between the PPP convergence and each of the residual measurement noise level and satellite geometry, a strategy for the selection of satellites (GPS and GALILEO) for PPP is developed and exploited. Tests using 24 hours of real data show that the two developments above contribute to the realisation of static PPP positioning accuracies of 40 cm (3D, 100%) within a convergence time of 20 minutes. Furthermore, based on simulated data, the same accuracy is achieved in kinematic mode but within a convergence time of one hour. These levels of performance represent significant improvements over the state-of-the-art (i.e. convergence time of twenty minutes instead of thirty for static users and one hour instead of hours for dynamic users). The potential of the use of multiple frequencies from modernised GPS and GALILEO on float ambiguity PPP is demonstrated with simulated data, and shown to have the potential to offer significant improvement in the availability of PPP in difficult user environments such as urban areas. Finally, the thesis addresses the potential application of PPP for mission (e.g. safety critical) applications and the need for integrity monitoring. An existing Carrier-phase Receiver Autonomous Integrity Monitoring (CRAIM) algorithm is implemented and shown to have the potential to protect PPP users against abnormally large errors